Virginia Gov. Terry McAuliffe’s top transportation officials Thursday put the state administration firmly behind an extensive program to ease travel conditions on Interstate 66, a program they estimate will cost $2 billion to $3 billion.

The effort — covering the 25-mile stretch of I-66 from the Capital Beltway west to Haymarket, in Prince William County — is still in the planning stages, but officials said construction could start in 2017.

State officials are very interested in adding this part of I-66 to the regional network of high-occupancy toll lanes. Three-person carpools would travel for free in these lanes while others would pay tolls. A HOT lanes program is attractive not only as a way of managing traffic congestion but also as a method of financing a package of improvements.

Other potential improvements are under study, including:

●Adding regular, untolled travel lanes.

●Extending Metrorail west to Centreville or Haymarket.

●Building light rail west from Vienna to either Centreville or Haymarket.

●Creating a bus rapid transit system from Vienna to Haymarket, possibly with an extension east from Vienna.

●Extending VRE rail service to Gainesville and Haymarket.

●Fixing choke points.

●Making it easier to transfer from one type of transport to another along the corridor.

■Improving safety.

●Upgrading the transportation communication system so that travelers have more real-time information about traffic conditions.

The McAuliffe administration did not originate the effort to do something about the congestion on I-66, a central artery that draws traffic from most major jurisdictions in Northern Virginia. And since McAuliffe (D) took office in January, his transportation leadership has been reevaluating several major projects elsewhere in Virginia.

But in their statements Thursday, members of the governor’s transportation team took ownership of the I-66 program.

Transportation Secretary Aubrey Layne, visiting the Virginia Department of Transportation’s Northern Virginia headquarters in Fairfax County, said the work on I-66 is “the number one project in Northern Virginia” and one of the most important in the state. “We are dedicated to getting the project to fruition,” Layne said.

Transportation officials pledged that the next phase of study — during which specific programs will be selected for development — will involve the public and be transparent. This phase would include the potential selection of private partners to design, build and operate some of those programs.

The state expects to have more transportation money flowing after last year’s changes in Virginia tax laws. Still, Layne said, a public-private partnership on the I-66 program is quite likely because of the high cost of achieving the major goals outlined in the initial, already completed study.

“I don’t believe the project will come to fruition if we use only tax dollars,” he said.

Layne also foresees a federal role in financing aspects of the program. He said he hoped Congress will resolve its dispute over long-term highway funding.

State officials said they don’t have to build everything at once. Constructing HOT lanes, for example, need not exclude the possibility of eventually extending Metro west. They acknowledged that the problems of moving people in the I-66 corridor are so complex that no one program is sufficient to address them.

A transportation program this extensive has as many political intricacies as engineering challenges.

Bob Chase, president of the Northern Virginia Transportation Alliance, an advocacy group, praised the administration for focusing on a program that would have a high impact on the entire region.

But state Sen. J. Chapman “Chap” Petersen (D-Fairfax County), who was among the officials at Thursday’s event, spotlighted another potentially high-impact question: Is the program going to enlarge the footprint of I-66 and require taking private property?

The state hasn’t figured that out yet, but the concept under study would replace the existing single high-occupancy vehicle lane in each direction with two HOT lanes — while maintaining the number of regular lanes. Designers can try to minimize the impact, but it definitely means a wider highway.